1,3,6-dioxazocan-2-ones and antimicrobial cationic polycarbonates therefrom

ABSTRACT

Eight-membered ring cyclic carbonates comprising a ring nitrogen at position 6 (1,3,6-dioxazocan-2-ones) were prepared by reaction of precursor diols with active carbonates. The ring nitrogen is linked to a pendant group Y′ via a methylene linking group. The cyclic carbonates undergo organocatalyzed ring opening polymerization to form an initial polycarbonate comprising a backbone tertiary amine group. Quaternization of the initial polycarbonates forms cationic polycarbonates comprising a positive-charged backbone quaternary nitrogen. The cationic polycarbonates can be potent antimicrobial agents.

PARTIES TO A JOINT RESEARCH AGREEMENT

This invention was made under a joint research agreement betweenInternational Business Machines Corporation and the Agency For Science,Technology and Research.

BACKGROUND

The present invention relates to 1,3,6-dioxazocan-2-ones andantimicrobial polycarbonates formed therefrom by organocatalyzed ringopening polymerization, and more specifically to antimicrobial cationicpolycarbonates comprising a quaternary nitrogen in the polycarbonatebackbone.

Current ring opening polymerizations of cyclic carbonates are limited bythe lack of main chain functionality in the polycarbonate other than thecarbonate functionality. The incorporation of heteroatoms (e.g.,nitrogen) in the polymer backbone is hampered by monomer instability.Heteroatom incorporation other than the carbonate oxygens within a7-membered ring or smaller ring monomer produces an unstable species(e.g., acetals, hemiaminals, and thioacetals for 6-membered and7-membered rings, and peroxides and N-oxides for 5-membered rings).

Cyclic carbonate monomers comprising a ring heteroatom in addition tothe carbonate oxygens are needed, in particular those comprising a ringnitrogen. Also needed are methods of ring opening polymerizations thatproduce polymers bearing a heteroatom other than carbonate oxygens.

SUMMARY

Accordingly, a compound is disclosed of formula (1):

wherein

ring positions are numbered 1 to 8,

each R′ is an independent monovalent radical selected from the groupconsisting of hydrogen and groups comprising 1 to 10 carbons, and

Y′ is a monovalent radical selected from the group consisting ofhydrogen and groups comprising 1 or more carbons.

Also disclosed is a method, comprising:

forming a mixture comprising, an organocatalyst, a solvent, anucleophilic initiator comprising one or more nucleophilic groupscapable of initiating a ring opening polymerization, an optionalaccelerator, and a compound of formula (1):

wherein

ring positions are numbered 1 to 8,

each R′ is an independent monovalent radical selected from the groupconsisting of hydrogen and groups comprising 1 to 10 carbons, and

Y′ is a monovalent radical selected from the group consisting ofhydrogen and groups comprising 1 or more carbons;

agitating the mixture, thereby forming an initial polymer by ringopening polymerization of the compound, the initial polymer comprising abasic repeat unit comprising a backbone carbonate group and a backbonetertiary nitrogen, the backbone nitrogen capable of reacting with aquaternizing agent to form a positive-charged backbone quaternarynitrogen; and

treating the initial polymer with the quaternizing agent, therebyforming a cationic polymer comprising a cationic repeat unit comprisingthe backbone carbonate group and the positive-charged backbonequaternary nitrogen, the quaternary nitrogen linked to 4 carbons.

Also disclosed is a cationic polymer having a structure according toformula (6):

I″-[Q′-E″]_(n′)  (6),

wherein

n′ is a positive integer greater than or equal to 1,

each Q′ is an independent divalent polymer chain comprising a cationicrepeat unit, wherein the cationic repeat unit comprises i) a backboneportion comprising a backbone carbonate group, ii) a positive-chargedbackbone quaternary nitrogen linked to 4 carbons, iii) a first sidechain portion having a structure *—CH₂—Y′, wherein the starred bond islinked to the backbone quaternary nitrogen, and Y′ is selected from thegroup consisting of hydrogen and groups comprising 1 or more carbons,and iv) a second side chain portion comprising 1 or more carbons,wherein one carbon of the second side chain portion is linked to thequaternary nitrogen,

I″ has a valency of n′, I″ comprises 1 or more carbons, and I″ comprisesn′ heteroatoms independently selected from the group consisting ofoxygen, nitrogen, and sulfur, wherein each of the heteroatoms is linkedto a respective Q′ terminal backbone carbonyl group,

each E″ is a monovalent second end group selected from the groupconsisting of hydrogen and moieties comprising 1 to 50 carbons, whereineach E″ is linked to a respective Q′ terminal backbone oxygen, and

the cationic polymer is an effective antimicrobial agent.

Further disclosed is a method of killing a microbe, comprisingcontacting the microbe with an above-described cationic polymer.

Also disclosed is a medical composition for treating wounds and/orinfections, comprising one or more of the above-described cationicpolymers.

Also disclosed is a cationic polymer of formula (8):

E″-Q′-I″-Q′-E″  (8),

wherein

each Q′ is an independent divalent polymer chain comprising a cationicrepeat unit, wherein the cationic repeat unit comprises i) a backboneportion comprising a backbone carbonate group, ii) a positive-chargedbackbone quaternary nitrogen linked to 4 carbons, iii) a first sidechain portion having a structure *—CH₂—Y′, wherein the starred bond islinked to the backbone quaternary nitrogen, and Y′ is selected from thegroup consisting of hydrogen and groups comprising 1 or more carbons,and iv) a second side chain portion comprising 1 or more carbons,wherein one carbon of the second side chain portion is linked to thequaternary nitrogen,

I″ is a divalent radical comprising 1 or more carbons, and I″ comprises2 heteroatoms independently selected from the group consisting ofoxygen, nitrogen, and sulfur, wherein each of the heteroatoms is linkedto a respective Q′ terminal backbone carbonyl group,

each E″ is an independent monovalent second end group selected from thegroup consisting of hydrogen and moieties comprising 1 to 50 carbons,wherein each E″ is linked to a respective Q′ terminal backbone oxygen.

The above-described and other features and advantages of the presentinvention will be appreciated and understood by those skilled in the artfrom the following detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph of number average molecular weight versus averagedegree of polymerization of polymers P-1 to P-4 (before quaternization).

FIG. 2 is a graph showing the % hemolysis of rat red blood cells as afunction of concentration (mg/L) of cationic polymer Examples 21 to 23(Q-1 to Q-3).

FIG. 3 is a bar graph showing the percent cell viability of HDF andHEK293 cells as a function of cationic polymer concentration.

FIG. 4 is a graph showing colony forming units/mL of Staphylococcusaureus (S. aureus) as a function of Q-3 concentration.

FIG. 5 is a graph showing colony forming units/mL of Escherichia coli(E. coli) as a function of Q-3 concentration.

FIG. 6 is a graph showing colony forming units/mL of Pseudomonasaeruginosa (P. aeruginosa) as a function of Q-3 concentration.

FIG. 7 is a graph showing colony forming units/mL of Candida albicans(C. albicans) as a function of Q-3 concentration.

FIG. 8 is a bar graph showing the killing efficiency of Q-3 against S.aureus.

FIG. 9 is a bar graph showing the killing efficiency of Q-3 against C.albicans.

FIG. 10 is a bar graph showing the killing efficiency of Q-3 against E.coli.

FIG. 11 is a bar graph showing the biomass of biofilms formed with E.coli and S. aureus as a function of Q-3 concentration (2, 4, 8, 10, 12,and 16×MIC).

FIG. 12 is a bar graph showing the cell viability of E. coli and S.aureus as a function of Q-3 concentration (2, 4, 8, 10, 12, and 16×MIC).

FIG. 13 is a magnification series of scanning electron micrograph (SEM)images of S. aureus cells after treatment for 2 hours with a lethal doseof Q-3.

FIG. 14 is a magnification series of SEM images of E. coli cells aftertreatment for 2 hours with a lethal dose of Q-3.

DETAILED DESCRIPTION

Disclosed are 1,3,6-dioxazocan-2-ones, hereinafter referred to as “firstcyclic monomers,” that undergo organocatalyzed ring openingpolymerization (ROP), thereby forming an initial polymer comprising atertiary nitrogen in the polymer backbone. Treating the initial polymerwith a suitable quaternizing agent produces a cationic polymercomprising a positive charged quaternary nitrogen in the cationicpolymer backbone. The cationic polymers can be potent antimicrobialagents against Gram-negative microbes, Gram-positive microbes, yeast,fungi, and combinations thereof.

The initial polymer comprises a basic repeat unit. The basic repeat unitcomprises a backbone portion (i.e., a portion of the initial polymerbackbone) and a side chain portion. The backbone portion of the basicrepeat unit comprises a carbonate group and a tertiary nitrogen linkedto three carbons. The side chain portion has a structure *—CH₂—Y′,wherein the starred bond is linked to the tertiary nitrogen and Y′ isselected from the group consisting of hydrogen and groups comprising 1or more carbons.

The initial polymer can be a homopolymer, random copolymer, or blockcopolymer comprising the basic repeat unit. The initial polymer caninclude one or more polymer chain segments comprising the basic repeatunit. At least one of the polymer chain segments comprises the basicrepeat unit. For example, each block of the block copolymer is a polymerchain segment that can be a homopolymer or copolymer, wherein at leastone block comprises the basic repeat unit. The initial polymer cancomprise the one or more polymer chain segments in a linear or branchedarrangement of repeat units. Branched structures can include starpolymers, graft polymers, brush polymers, mikto-arm polymers anddendritic polymers.

The cationic polymer comprises a cationic repeat unit. The cationicrepeat unit comprises a backbone portion (i.e., a portion of thecationic polymer backbone), a first side chain portion and a second sidechain portion. The backbone portion of the cationic repeat unitcomprises a backbone carbonate group and a backbone positive-chargedquaternary nitrogen, which is covalently bonded to four carbons. Thequaternary nitrogen of the backbone is not covalently bonded to anyhydrogen. The positive-charged quaternary nitrogen is linked to a carbonof the first side chain portion and to a carbon of the second side chainportion. The first side chain portion has a structure *—CH₂—Y′, whereinthe starred bond is linked to the quaternary nitrogen. The second sidechain portion is a moiety comprising at least one carbon.

The cationic polymer can be a homopolymer, random copolymer, or blockcopolymer comprising the basic repeat unit. The cationic polymer caninclude one or more polymer chain segments, wherein at least one of thepolymer chain segments comprises the cationic repeat unit. For example,each block of the block copolymer can be a homopolymer or a copolymer,wherein at least one block comprises the cationic repeat unit. Thecationic polymer can comprise the one or more polymer chain segments ina linear or branched arrangement of repeat units. Branched structurescan include star polymers, graft polymers, brush polymers, dendriticpolymers, mikto-arm polymers and the like.

More specifically, the first cyclic monomers have a structure accordingto formula (1):

wherein

ring positions are numbered 1 to 8,

each R′ is an independent monovalent radical selected from the groupconsisting of hydrogen and groups comprising 1 to 10 carbons, and

Y′ is a monovalent radical selected from the group consisting ofhydrogen and groups comprising 1 or more carbons.

The tertiary nitrogen at ring position 6 is bonded to three carbons asshown in formula (1). In an embodiment, each R′ is hydrogen.

Non-limiting examples of Y′ include hydrogen, methyl, ethyl, propyl,phenyl, and substituted phenyl. Y′ can include additional functionalitysuch as, for example, ester, amide, carbamate, thioester, ketone, ether,amine, nitrogen-containing heterocycle, oxygen-containing heterocycle,olefin, acetylene, nitrile, bicyclic rings, and combinations thereof.

Non-limiting examples of *—CH₂Y′ groups include methyl, ethyl, propyl,butyl, benzyl, and substituted benzyl.

The first cyclic monomers can be prepared from amine-diols of formula(2):

wherein

each R′ is an independent monovalent radical selected from the groupconsisting of hydrogen and groups comprising 1 to 10 carbons, and

Y′ is a monovalent radical selected from the group consisting ofhydrogen and groups comprising 1 or more carbons.

The first cyclic monomers can be prepared by treating an amine-diol offormula (2) with a carbonate forming compound. Although a base catalystis not essential; the reaction is preferably conducted using a base(e.g., triethylamine).

Non-limiting carbonate forming compounds include phosgene, triphosgene,ethylchloroformate, diphenylcarbonate, bis-(pentafluorophenyl)carbonate,bis-(pentachlorophenyl)carbonate, and the like.

The first cyclic monomers undergo organocatalyzed ring openingpolymerization (ROP) to form the initial polymer. The ROP can includeother cyclic carbonyl monomers, including cyclic carbonates and/orcyclic esters that can serve as diluents (comonomers) for the firstcyclic monomers. As non-limiting examples, a polymer chain segment ofthe initial polymer can be a polycarbonate copolymer comprising two ormore different carbonate repeat units, or a polyestercarbonatecopolymer, comprising at least one carbonate repeat unit and one esterrepeat unit.

The first cyclic monomer can be stereospecific or non-stereospecific.

Initial Polymers

The initial polymer can have a structure according to formula (3):

wherein

n′ is an positive integer greater than or equal to 1,

each P′ is a divalent polymer chain comprising one or more polymer chainsegments, a terminal backbone carbonyl group, and a terminal backboneoxygen, wherein at least one of the polymer chain segments comprises abasic carbonate repeat unit,

I′ is a radical having a valency of 1 or more, wherein I′ comprises 1 ormore carbons,

the backbone carbonyl group of each P′ is linked to a respectiveindependent heteroatom of I′ selected from the group consisting ofoxygen, nitrogen, and sulfur;

the basic carbonate repeat unit comprises a backbone portion and a firstside chain portion, the backbone portion comprising a backbone carbonategroup and a backbone tertiary nitrogen, the first side chain portionhaving a structure *—CH₂—Y′, wherein the starred bond is linked to thebackbone tertiary nitrogen and Y′ is selected from the group consistingof hydrogen and groups comprising 1 or more carbons,

E′ is a monovalent second end group selected from the group consistingof hydrogen and moieties comprising 1 to 50 carbons, and

the terminal backbone oxygen of each P′ is linked to a respective E′.

I′ can be a residue of a nucleophilic initiator for an organocatalyzedROP of the first cyclic monomers, wherein the nucleophilic initiatorcomprises n nucleophilic sites capable of initiating the ROP, and n′polymer chains P′ are formed by the ROP.

Each P′ can be a homopolymer, random copolymer, or block copolymercomprising the basic repeat unit. Each P′ can have an average degree ofpolymerization (DP) of more than 1 to about 200. In an embodiment, n′=1and the initial polymer comprises one polymer chain P′ having an averageDP of about 20 to about 100.

The initial polymer can comprise basic repeat units singularly or incombination. P′ can further comprise repeat units derived from cycliccarbonate and/or cyclic ester monomers other than the first cyclicmonomers.

Each P′ preferably has a linear arrangement of repeat units (i.e., eachP′ is a linear polymer chain comprising one polymer branch as opposed tointersecting polymer branches). When P′ contains two or more polymerchain segments (e.g., as a diblock copolymer chain), the different chainsegments are linked by their respective chain ends, no more than twopolymer chain ends are linked together by a given linking group, and therespective polymer chain segments are not linked together in the form ofa cyclic polymer structure.

I′ can be a residue of a nucleophilic initiator for the organocatalyzedring opening polymerization used to form P′, or a derivative of theresidue. Preferably, I′ comprises n′ number of independent heteroatomsselected from the group consisting of an oxygen, nitrogen, and sulfur,wherein each of the heteroatoms is linked in the form of a carbonate,carbamate or thiocarbonate group to a respective P′ terminal backbonecarbonyl group′ (i.e., to the “carbonyl end” of P′).

I′ can comprise a biologically active moiety such as, for example asteroid group and/or a vitamin. I′ can comprise a polymer such as, forexample a poly(ethylene oxide) chain segment. In an embodiment, I′ is aresidue of a mono-endcapped mono-nucleophilic polyethylene oxideinitiator (e.g., mono-methylated polyethylene glycol (mPEG)). In anotherembodiment, I′ comprises 1 to 50 carbons. In yet another embodiment, I′is an alkoxy or aryloxy group comprising 1 to 10 carbons.

Each E′ is preferably linked to a terminal backbone oxygen at theopposing end of a respective polymer chain P′, referred to herein as the“oxy end” of P′. When E′ is hydrogen, P′ has a terminal hydroxy group(i.e., a living chain end capable of initiating another ring openingpolymerization). When E′ is not hydrogen, E′ can be any suitable endgroup comprising 1 to 50 carbons. In an embodiment, E′ is an acyl groupcomprising 1 to 15 carbons (e.g., acetyl group).

The basic repeat unit of the initial polymer has a structure accordingto formula (4):

wherein

backbone atoms of the basic repeat unit are numbered 1 to 8,

the starred bonds represent attachment points to other repeat unitsand/or end groups of the initial polymer,

each R′ is an independent monovalent radical selected from the groupconsisting of hydrogen and groups comprising 1 to 10 carbons, and

*—CH₂—Y′ is a first side chain, wherein Y′ is a monovalent radicalselected from the group consisting of hydrogen, and groups comprising 1or more carbons.

The tertiary nitrogen of formula (4) is bonded to two backbone carbonslabeled 5 and 7 and to the methylene carbon of the first side chain*—CH₂—Y′. In an embodiment, each R′ is hydrogen.

In an embodiment, n′=1. A non-limiting example of an initial polymer offormula (4) wherein n′=1 is the polycarbonate A-1:

In this example, the initial polymer A-1 has one polymer chain P′ whichhas one polymer chain segment. In this example, P′ is a polycarbonatehomopolymer of the basic repeat unit shown in parentheses. A-1 has alinear polymer arrangement of the basic repeat units, which are linkedin a head-to-tail arrangement, wherein carbon 2 represents the head, andoxygen 3 represents the tail. Polymer chain P′ of A-1 has two polymerchain ends linked to respective end groups I′ and E′. The carbonyl endand oxy end of P′ are indicated by arrows. The basic repeat unit of A-1has a structure according to formula (4) wherein each R′ is H and Y′ isphenyl. The first end group I′ is benzyloxy, and the second end group E′is hydrogen. Subscript n′ represents the degree of polymerization, andhas an average value of 2 to 200. A-1 has a living end containing aprimary alcohol, which can potentially initiate a ring openingpolymerization.

Another more specific initial polymer comprises two polymer chains P′(n′=2 in formula (4)). In this instance, the initial polymer can have astructure in accordance with formula (5):

E^(a)-P^(a)-I^(a)-P^(b)-E^(b)  (5),

wherein

P^(a) is a first divalent polymer chain comprising one or more polymerchain segments, wherein at least one of the polymer chain segmentscomprises a basic repeat unit,

P^(b) is a second divalent polymer chain comprising one or more polymerchain segments, wherein at least one of the polymer chain segmentscomprises a basic carbonate repeat unit,

the basic carbonate repeat unit comprises a backbone portion and a firstside chain portion, the backbone portion comprising a backbone carbonategroup and a backbone tertiary nitrogen, the first side chain portionhaving a structure *—CH₂—Y′, wherein the starred bond is linked to thebackbone tertiary nitrogen and Y′ is selected from the group consistingof hydrogen and groups comprising 1 or more carbons,

I^(a) is a divalent linking group covalently bound to the respectivecarbonyl ends of P^(a) and P^(b),

E^(a) is a monovalent first end group selected from the group consistingof hydrogen and moieties comprising 1 to 50 carbons, wherein E^(a) islinked to the oxy end of P^(a), and

E^(b) is a monovalent second end group selected from the groupconsisting of hydrogen and moieties comprising 1 to 50 carbons, whereinE^(b) is linked to the oxy end of P^(b).

P^(a) can have an average degree of polymerization of more than 1 toabout 200. P^(a) can be a homopolymer, random copolymer, or blockcopolymer comprising the basic repeat unit.

P^(b) can have an average degree of polymerization of more than 1 toabout 200. P^(b) can be a homopolymer, random copolymer, or blockcopolymer comprising the basic repeat unit.

In an embodiment, I^(a) is a residue of a di-nucleophilic initiator forthe organocatalyzed ring opening polymerization used to prepareE^(a)-P^(a)-I^(a)-P^(b)-E^(b). In this instance, I^(a) comprises twoheteroatoms independently selected from oxygen, nitrogen, and sulfur,wherein the two heteroatoms are independently linked in the form ofcarbonate, carbamate, or thiocarbonate groups to respective carbonylends of P^(a) and P^(b). I^(a) can be a derivative of the residue of thedi-nucleophilic initiator for the ROP.

I^(a) can comprise a polymer such as, for example, a divalentpoly(ethylene oxide) chain. I^(a) can comprise a biologically activegroup such as a steroid and/or a vitamin. In an embodiment, I^(a) is aresidue of a di-nucleophilic polyethylene glycol initiator for the ROP.In another embodiment, I^(a) comprises 1 to 50 carbons. In anotherembodiment, I^(a) is a residue of an ester of 2,2-dimethylol propionicacid.

E^(a) is linked to the oxy end of P^(a). When E^(a) is hydrogen, P^(a)has a terminal hydroxy group (i.e., a living chain end potentiallycapable of initiating another ring opening polymerization). When E^(a)is not hydrogen, E^(a) can be any suitable end group comprising 1 to 50carbons. In an embodiment, E^(a) is an acyl group comprising 1 to 10carbons.

E^(b) is linked to the oxy end of P^(b). When E^(b) is hydrogen, P^(b)has a terminal hydroxy group (i.e., a living chain end potentiallycapable of initiating another ring opening polymerization). When E^(b)is not hydrogen, E^(b) can be any suitable end group comprising 1 to 50carbons. In an embodiment, E^(b) is an acyl group comprising 1 to 10carbons.

A non-limiting example of an initial polymer of formula (5) is A-2:

The initial polymer A-2 is a linear polymer containing two polymerchains linked by respective chain ends to divalent linking group I^(a).Each polymer chain P^(a) and P^(b) of A-2 is a polycarbonate homopolymerof the basic repeat unit in parentheses. The carbonyl ends and oxy endsof each polymer chain P^(a) and P^(b) are labeled in A-2. The basicrepeat unit of each polymer chain has a structure according to formula(4), wherein each R′ is H and Y′ is phenyl. I^(a) is benzyl2,2-bis(oxymethylene)propionate, E^(a) is hydrogen, and E^(b) ishydrogen. Subscripts a′ and b′ represent degree of polymerization andindependently have average values of more than 1 to about 200. Theinitial polymer A-2 has two living ends containing primary alcohols,each potentially capable of initiating a ring opening polymerization.

The initial polymers can be stereospecific or non-stereospecific.

Cationic Polymers

When treated with a suitable amine quaternizing agent, the initialpolymers form cationic polymers comprising cationic repeat units. Thecationic repeat units comprise a positive-charged backbone quaternarynitrogen linked to 4 carbons.

Quaternization of initial polymers of structure I′-[P′-E′]_(n′) producescationic polymers having a structure in accordance with formula (6):

I″-[Q′-E″]_(n′)  (6),

wherein

n′ is a positive integer greater than or equal to 1,

each Q′ is an independent divalent polymer chain comprising a cationicrepeat unit, wherein the cationic repeat unit comprises i) a backboneportion comprising a backbone carbonate group, ii) a positive-chargedbackbone quaternary nitrogen linked to 4 carbons, iii) a first sidechain portion having a structure *—CH₂—Y′, wherein the starred bond islinked to the backbone quaternary nitrogen, and Y′ is selected from thegroup consisting of hydrogen and groups comprising 1 or more carbons,and iv) a second side chain portion comprising 1 or more carbons,wherein one carbon of the second side chain portion is linked to thequaternary nitrogen,

I″ has a valency of n′, I″ comprises 1 or more carbons, and I″ comprisesn′ heteroatoms independently selected from the group consisting ofoxygen, nitrogen, and sulfur, wherein the heteroatoms are linked torespective Q′ terminal backbone carbonyl groups,

each E″ is a monovalent second end group selected from the groupconsisting of hydrogen and moieties comprising 1 to 50 carbons, whereineach E″ is linked to a respective Q′ terminal backbone oxygen.

Each Q′ can have an average degree of polymerization of more than one toabout 200. Each Q′ can be a homopolymer, random copolymer, or blockcopolymer comprising the cationic repeat unit.

The cationic polymer can comprise the cationic repeat units singularlyor in combination. Each Q′ can further comprise additional repeat unitsderived from cyclic carbonate and/or cyclic ester comonomers, which canact as diluents for the cationic repeat unit.

Each Q′ preferably has a linear arrangement of repeat units (i.e., eachQ′ is a linear polymer chain comprising one polymer branch as opposed tointersecting polymer branches). When Q′ contains two or more polymerchain segments (e.g., as a diblock copolymer chain), the different chainsegments are linked by their respective chain ends, no more than twopolymer chain ends are linked together by a given linking group, and therespective polymer chain segments are not linked together in the form ofa cyclic polymer structure.

I″ can be a residue of a nucleophilic initiator for the ring openingpolymerization used to form the basic initial polymer, I′-[P′-E′]_(n′),which serves as a precursor to the cationic polymer. I″ can be aderivative of the residue of a nucleophilic initiator. Each of theabove-described heteroatoms of I″ is linked in the form of carbonate,carbamate or thiocarbonate group to a respective Q′ terminal backbonecarbonyl group′ (i.e., the carbonyl end of a Q′).

I″ can comprise a biologically active moiety such as, for example, asteroid group and/or a vitamin. I″ can comprise a polymer such as, forexample a poly(ethylene oxide) chain segment. In an embodiment, I″ is aresidue of a mono-endcapped mono-nucleophilic polyethylene oxideinitiator (e.g., mono-methylated polyethylene glycol (mPEG)). In anotherembodiment, I″ comprises 1 to 50 carbons. In another embodiment, I″ isan alkoxy or aryloxy group comprising 1 to 10 carbons. In anotherembodiment, I″ is the same as I′.

Each E″ is linked to a terminal backbone oxygen at the opposing end of arespective polymer chain Q′ (i.e., to the oxy end of Q′). When E″ ishydrogen, Q′ has a terminal hydroxy group (i.e., a living chain endcapable of initiating another ring opening polymerization). When E″ isnot hydrogen, E″ can be any suitable end group comprising 1 to 50carbons. In an embodiment, E″ is an acyl group comprising 1 to 15carbons. In another embodiment, E″ is the same as E′.

The cationic repeat unit of the cationic polymer has a structureaccording to formula (7):

wherein

cationic polymer backbone atoms are numbered 1 to 8,

the starred bonds represent attachment points to other repeat unitsand/or end groups of the cationic polymer,

each R′ is an independent monovalent radical selected from the groupconsisting of hydrogen and groups comprising 1 to 10 carbons,

R″ is a group comprising 1 or more carbons, wherein one carbon of R″ isbonded to the positive charged nitrogen labeled 6,

Y′ is a monovalent radical selected from the group consisting ofhydrogen, and groups comprising 1 or more carbons, and

X^(⊖) is a negative-charged counterion.

The quaternary nitrogen of formula (7) is bonded to 4 carbons: carbonslabeled 5 and 7, the methylene carbon of side chain *—CH₂—Y′, and onecarbon of R″. In an embodiment, each R′ is hydrogen.

X^(⊖) can be any suitable negative-charged counterion. In an embodiment,X^(⊖) is selected from the group consisting of chloride, bromide, andiodide. X^(⊖) counterions can be presented singularly or in combination.

In an embodiment, n′=1. A non-limiting example of a cationic polymer offormula (6) wherein n′=1 is the polycarbonate A-3:

A-3 has one polymer chain Q′ comprising one polymer chain segment. Inthis example, Q′ is a polycarbonate homopolymer of the cationic repeatunit shown in parentheses. A-3 has a linear polymer structure. Polymerchain Q′ of A-1 has two polymer chain ends linked to respective endgroups I″ and E″. The carbonyl end and oxy end of Q′ are indicated byarrows. The cationic repeat unit of A-3 has a structure according toformula (7), wherein each R′ is H, R″ is methyl, X^(⊖) is chloride ion,and Y′ is phenyl. The first end group I″ is benzyloxy, and the secondend group E″ is hydrogen. Subscript n′ represents the degree ofpolymerization and has an average value of 2 to 200. A-3 has a livingend containing a primary alcohol, which can potentially initiate a ringopening polymerization.

Another more specific cationic polymer comprises two polymer chains Q′(n′=2 in formula (6)). In this instance, the cationic polymer can have astructure in accordance with formula (8):

E″-Q′-I″-Q′-E″  (8),

wherein

each Q′ is an independent divalent polymer chain comprising a cationicrepeat unit, wherein the cationic repeat unit comprises i) a backboneportion comprising a backbone carbonate group, ii) a positive-chargedbackbone quaternary nitrogen linked to 4 carbons, iii) a first sidechain portion having a structure *—CH₂—Y′, wherein the starred bond islinked to the backbone quaternary nitrogen, and Y′ is selected from thegroup consisting of hydrogen and groups comprising 1 or more carbons,and iv) a second side chain portion comprising 1 or more carbons,wherein one carbon of the second side chain portion is linked to thequaternary nitrogen,

I″ is a divalent radical comprising 1 or more carbons, and I″ comprises2 heteroatoms independently selected from the group consisting ofoxygen, nitrogen, and sulfur, wherein each of the heteroatoms is linkedto a respective Q′ terminal backbone carbonyl group,

each E″ is an independent monovalent second end group selected from thegroup consisting of hydrogen and moieties comprising 1 to 50 carbons,wherein each E″ is linked to a respective Q′ terminal backbone oxygen.

Each Q′ of formula (8) can have an average degree of polymerization ofmore than 1 to about 200. Each Q′ can be a homopolymer, randomcopolymer, or block copolymer comprising the cationic repeat unit.

I″ can comprise a polymer such as, for example, a divalent poly(ethyleneoxide) chain. I″ can comprise a biologically active group such as asteroid and/or a vitamin. In an embodiment, I″ is a residue of adi-nucleophilic polyethylene glycol (PEG) initiator for the ROP. Inanother embodiment, I″ comprises 1 to 50 carbons. In another embodiment,I″ is a residue of an ester of 2,2-dimethylol propionic acid. In anotherembodiment, I″ is the same as I^(a).

Each E″ is linked to the oxy end of a respective Q′.

A non-limiting example of a cationic polymer of formula (8) is A-4:

The cationic polymer A-4 is a linear polymer containing two polymerchains Q′ linked by respective carbonyl ends to divalent linking groupI″. Each polymer chain Q′ is a polycarbonate homopolymer of the cationicrepeat unit in parentheses. The carbonyl ends and oxy ends of eachpolymer chain are labeled in A-4. The cationic repeat unit of each Q′has a structure according to formula (7) wherein each R′ is H, Y′ isphenyl, R″ is methyl, and X^(e) is chloride. In this example, I″ isbenzyl 2,2-bis(oxymethylene)propionate, and each E″ is hydrogen.Subscripts a′ and b′ represent degree of polymerization and have averagevalues of more than 1 to about 200. The cationic polymer A-4 has twoliving ends containing primary alcohol groups, which are potentiallycapable of initiating a ring opening polymerization.

The cationic polymers can be stereospecific or non-stereospecific.

Biologically Active Compounds

E′, E″, I′, and/or I″ can comprise a covalently bound form of abiologically active compound, referred to herein as a biologicallyactive moiety. Biologically active compounds include steroids andvitamins. In an embodiment, the biologically active compound is selectedfrom the group consisting of cholesterol, alpha-tocopherol (a vitamin Ecompound), ergocalciferol (vitamin D2), and combinations thereof.

As a non-limiting example, I′ of the initial polymer of formula (3) canhave a structure S′-L′-* wherein S′ is a steroid group (e.g., acholesteryl group) and L′ is a single bond or any suitable divalentlinking group comprising 1 to about 10 carbons. In this instance, L′links S′ to the carbonyl end of P′. The steroid group can enhance biocompatibility of the cationic polymer.

The steroid group S′ can originate from a naturally occurring humansteroid, non-human steroid, and/or a synthetic steroid compound. Herein,a steroid group comprises a tetracyclic ring structure:

wherein the 17 carbons of the ring system are numbered as shown. Thesteroid group can comprise one or more additional substituents attachedto one or more of the numbered ring positions. Each ring of thetetracyclic ring structure can independently comprise one or more doublebonds.

Exemplary steroid groups include cholesteryl, from cholesterol, shownbelow without stereochemistry:

Non-limiting stereospecific structures of cholesteryl include

where the R,S stereoconfiguration of each stereospecific asymmetriccenter is labeled.

Additional non-limiting steroid groups include

The starred bonds represent attachment points. For example, the starredbond of each of the above steroid groups can be linked to a terminalcarbonyl group of the initial polymer backbone and/or the cationicpolymer backbone by way of a divalent linking group L′. Alternatively,the starred bond of the steroid group can be directly linked to aterminal carbonyl group of the initial polymer backbone and/or cationicpolymer backbone (i.e., L′ can be a single bond).

Each asymmetric center of a steroid group can be present as the Rstereoisomer, S stereoisomer, or as a mixture of R and S stereoisomers.Additional steroid groups S′ include the various stereoisomers of theabove structures. The cationic polymer can comprise a steroid group as asingle stereoisomer or as a mixture of stereoisomers.

In an embodiment, S′ is cholesteryl group, wherein the cholesteryl groupis a mixture of isomers

indicated by the structure

When L′ is a single bond, S′ is linked directly to the terminal carbonylgroup of the polycarbonate backbone. In an embodiment, L′ is a divalentlinking group comprising an alkylene oxide selected from the groupconsisting of ethylene oxide (*—CH₂CH₂O—*), propylene oxide*—CH₂CH₂CH₂O—*, and/or tri(ethylene oxide) (*—CH₂CH₂OCH₂CH₂OCH₂CH₂O—*),wherein the starred bond of the oxygen is linked to the terminalcarbonyl group of the initial polymer backbone and/or cationic polymerbackbone and the starred bond of the carbon is linked to S′.

Ring Opening Polymerization

A preferred method of preparing the disclosed cationic polymerscomprises agitating a first mixture comprising a first cyclic monomer offormula (1), a nucleophilic initiator, an organocatalyst, an optionalaccelerator, and a solvent, thereby forming an initial polymer by a ringopening polymerization, wherein the initial polymer comprises a basicrepeat unit of formula (4). Optionally, the first mixture can include acyclic carbonyl comonomer selected from cyclic carbonates, cyclicesters, and combinations thereof. Treating the initial polymer with asuitable tertiary amine quaternizing agent forms a cationic polymercomprising a cationic repeat unit of formula (7).

The ring-opening polymerization can be performed at a temperature thatis about ambient temperature or higher, more specifically 15° C. to 200°C., and even more specifically 20° C. to 80° C. Preferably, the ROP isperformed at ambient temperature. Reaction times vary with solvent,temperature, agitation rate, pressure, and equipment, but in general thepolymerizations are complete within 1 to 100 hours.

The ROP polymerization is conducted under an inert dry atmosphere, suchas nitrogen or argon, and at a pressure of 100 MPa to 500 MPa (1 atm to5 atm), more typically at a pressure of 100 MPa to 200 MPa (1 atm to 2atm). At the completion of the reaction, the solvent can be removedusing reduced pressure.

Solvents

The ROP reaction can be performed with or without a solvent. Preferably,the ROP is performed using a solvent. Non-limiting solvents includedichloromethane, chloroform, benzene, toluene, xylene, chlorobenzene,dichlorobenzene, benzotrifluoride, petroleum ether, acetonitrile,pentane, hexane, heptane, 2,2,4-trimethylpentane, cyclohexane, diethylether, t-butyl methyl ether, diisopropyl ether, dioxane,tetrahydrofuran, or a combination comprising one of the foregoingsolvents. A suitable monomer concentration is about 0.1 to 5 moles perliter, and more particularly about 0.2 to 4 moles per liter.

Comonomers

Non-limiting examples of cyclic carbonate comonomers include thecompounds of Table 1. These can be used, for example, to form randomcopolymers or block copolymers with the first cyclic monomer(s).

TABLE 1

Non-limiting examples of cyclic ester comonomers include the compoundsof Table 2.

TABLE 2

Initiators for the ROP

Initiators for the ROP generally include alcohols, amines, and/orthiols. The initiator can comprise one or more nucleophilic groupscapable of initiating a ring opening polymerization of the first cyclicmonomer.

For the above described cationic polymers having one cationic polymerchain, the ROP initiator can be a mono-nucleophilic initiator comprising1 to 50 carbons (e.g., ethanol, n-butanol, benzyl alcohol). The ROPinitiator can be a biologically active compound selected from the groupconsisting of steroids, vitamins, and combinations thereof. For example,mono-nucleophilic ROP initiators include cholesterol, alpha-tocopherol,and ergocalciferol.

Other mono-nucleophilic ROP initiators comprise a covalently bound formof a biologically active compound. For example, the initiator can have astructure according to formula (I-1):

S′-L^(e)  (I-1),

wherein S′ is a steroid moiety or vitamin moiety, and L^(e) is amonovalent group comprising i) 1 to about 10 carbons and ii) anucleophilic initiating group for the ROP. Non-limiting examples of ROPinitiators of formula (I-1) include Chol-OPrOH:

and Chol-OTEG-OH:

In the above examples, S′ is a cholesteryl group.

The residue of the ROP initiator S′-L^(e) initiator is denoted byS′-L′-*, which is linked to the carbonyl end of the initial polymerbackbone. The S′-L′-* residue of Chol-OPrOH has the structure:

The S′-L′-* residue of Chol-OTEG-OH has the structure:

The initiator can be a mono-nucleophilic polyether initiator. Exemplarymono-nucleophilic polyether initiators include mono-endcappedpoly(ethylene glycols) (e.g., mono-methyl poly(ethylene glycol)(mPEG-OH)) and mono-endcapped polypropylene glycols). The polymericinitiator can comprise a nucleophilic chain end group independentlyselected from the group consisting alcohols, primary amines, secondaryamines, and thiols.

The number average molecular weight (Mn) of the polyether initiator canbe from 100 to 10000, and even more specifically, 1000 to 5000.

The ROP initiator can be used singularly or in combination with adifferent ROP initiator (e.g., initiators having different steroidgroups and/or different L^(e) groups.) The ROP initiator can bestereospecific or non-stereospecific.

The ROP initiator used to form cationic polymers having two polymerchains is a di-nucleophilic initiator. Exemplary di-nucleophilic ROPinitiators include ethylene glycol, butanediol, 1,4-benzenedimethanol,and BnMPA:

An exemplary di-nucleophilic ROP initiator comprising a steroid group isChol-MPA:

Exemplary di-nucleophilic polyether ROP initiators include poly(ethyleneglycol) (referred to as PEG or HO-PEG-OH) having the structureHO—[CH₂CH₂O]_(n)—H and poly(propylene glycol) (referred to as PPG orHO-PPG-OH) having the structure HO—[CH₂C(H)(CH₃)O]_(n)—H, andcopolyethers comprising ethylene oxide and propylene oxide repeat units.The number average molecular weight (Mn) of the dinucleophilic polyetherinitiator can be from 100 to 10000, and even more specifically, 1000 to5000.

Initiators comprising 3 or more nucleophilic groups can be used togenerate star polymers, graft polymers, and the like, which comprise 3or more polymer chains Q′.

Endcap Agents

The living end (oxy end) of the initial polymer formed by the ROP has areactive hydroxy group (second end group E′=H), which is capable ofinitiating another ROP. The living end can be treated with an endcapagent, thereby forming a different end group E′, which is capable ofpreventing further chain growth and/or stabilizing the polymer againstunwanted side reactions such as chain scission. The polymerization andendcapping can occur in the same pot without isolating the initialpolymer. Endcap agents include, for example, materials for convertingterminal hydroxy groups to esters, such as carboxylic acid anhydrides,carboxylic acid chlorides, and reactive esters (e.g., p-nitrophenylesters). In an embodiment, the endcap agent is an acylating agent, andthe second end group E′ is an acyl group. In another embodiment theacylating agent is acetic anhydride, and the end group E′ is an acetylgroup. In another embodiment, the endcap agent comprises a covalentlybound form of a steroid group, a vitamin, or a combination thereof.

Quaternizing Agents

No restriction is placed on the quaternizing agent. Exemplarynon-limiting quaternizing agents include alkyl halides, alkylsulfonates, and the like. The quaternizing agent can include acovalently bound form of a biologically active compound such as, forexample a steroid, vitamin, and/or drug.

ROP Catalysts

Less preferred catalysts for a ROP polymerization include metal oxidessuch as tetramethoxy zirconium, tetra-iso-propoxy zirconium,tetra-iso-butoxy zirconium, tetra-n-butoxy zirconium, tetra-t-butoxyzirconium, triethoxy aluminum, tri-n-propoxy aluminum, tri-iso-propoxyaluminum, tri-n-butoxy aluminum, tri-iso-butoxy aluminum, tri-sec-butoxyaluminum, mono-sec-butoxy-di-iso-propoxy aluminum, ethyl acetoacetatealuminum diisopropylate, aluminum tris(ethyl acetoacetate), tetraethoxytitanium, tetra-iso-propoxy titanium, tetra-n-propoxy titanium,tetra-n-butoxy titanium, tetra-sec-butoxy titanium, tetra-t-butoxytitanium, tri-iso-propoxy gallium, tri-iso-propoxy antimony,tri-iso-butoxy antimony, trimethoxy boron, triethoxy boron,tri-iso-propoxy boron, tri-n-propoxy boron, tri-iso-butoxy boron,tri-n-butoxy boron, tri-sec-butoxy boron, tri-t-butoxy boron,tetramethoxy germanium, tetraethoxy germanium, tetra-iso-propoxygermanium, tetra-n-propoxy germanium, tetra-iso-butoxy germanium,tetra-n-butoxy germanium, tetra-sec-butoxy germanium and tetra-t-butoxygermanium; halogenated compounds such as antimony pentachloride, zincchloride, lithium bromide, tin(IV) chloride, cadmium chloride and borontrifluoride diethyl ether; alkyl aluminum such as trimethyl aluminum,triethyl aluminum, diethyl aluminum chloride, ethyl aluminum dichlorideand tri-iso-butyl aluminum; alkyl zinc such as dimethyl zinc, diethylzinc and diisopropyl zinc; heteropolyacids such as phosphotungstic acid,phosphomolybdic acid, silicotungstic acid and alkali metal saltsthereof; zirconium compounds such as zirconium acid chloride, zirconiumoctanoate, zirconium stearate, and zirconium nitrate.

Preferably, the chemical formula of the catalyst used for the ringopening polymerization does not include an ionic or nonionic form of ametal selected from the group consisting of beryllium, magnesium,calcium, strontium, barium, radium, aluminum, gallium, indium, thallium,germanium, tin, lead, arsenic, antimony, bismuth, tellurium, polonium,and metals of Groups 3 to 12 of the Periodic Table. Metals of Groups 3to 12 of the Periodic Table include scandium, titanium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium,zirconium, niobium, molybdenum, technetium, ruthenium, rhodium,palladium, silver, cadmium, lanthanum, cerium, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, lutetium, hafnium, tantalum,tungsten, rhenium, osmium, iridium, platinum, gold, mercury, actinium,thorium, protactinium, uranium, neptunium, plutonium, americium, curium,berkelium, californium, einsteinium, fermium, mendelevium, nobelium,lawrencium, rutherfordium, dubnium, seaborgium, bohrium, hassium,meitnerium, darmstadtium, roentgenium, and copernicium.

Preferred catalysts are organocatalysts whose chemical formulas containnone of the above metals. Examples of organocatalysts for ring openingpolymerizations include tertiary amines such as triallylamine,triethylamine, tri-n-octylamine and benzyldimethylamine4-dimethylaminopyridine, phosphines, N-heterocyclic carbenes (NHC),bifunctional aminothioureas, phosphazenes, amidines, and guanidines.

A more specific organocatalyst isN-bis(3,5-trifluoromethyl)phenyl-N′-cyclohexylthiourea (TU):

Other ROP organocatalysts comprise at least one1,1,1,3,3,3-hexafluoropropan-2-ol-2-yl (HFP) group. Singly-donatinghydrogen bond catalysts have the formula (28):

R²—C(CF₃)₂OH  (C-1),

wherein R² represents a hydrogen or a monovalent radical having 1 to 20carbons, for example an alkyl group, substituted alkyl group, cycloalkylgroup, substituted cycloalkyl group, heterocycloalkyl group, substitutedheterocycloalkyl group, aryl group, substituted aryl group, or acombination thereof. Exemplary singly-donating hydrogen bondingcatalysts are listed in Table 3.

TABLE 3

Doubly-donating hydrogen bonding catalysts have two HFP groups,represented by the formula (29):

wherein R³ is a divalent radical bridging group comprising 1 to 20carbons, such as an alkylene group, a substituted alkylene group, acycloalkylene group, substituted cycloalkylene group, aheterocycloalkylene group, substituted heterocycloalkylene group, anarylene group, a substituted arylene group, and a combination thereof.Representative double hydrogen bonding catalysts of formula (C-2)include those listed in Table 4. In a specific embodiment, R² is anarylene or substituted arylene group, and the HFP groups occupypositions meta to each other on the aromatic ring.

TABLE 4

In one embodiment, the catalyst is selected from the group consisting of4-HFA-St, 4-HFA-Tol, HFTB, NFTB, HPIP, 3,5-HFA-MA, 3,5-HFA-St, 1,3-HFAB,1,4-HFAB, and combinations thereof.

Also contemplated are catalysts comprising HFP-containing groups boundto a support. In one embodiment, the support comprises a polymer, acrosslinked polymer bead, an inorganic particle, or a metallic particle.HFP-containing polymers can be formed by known methods including directpolymerization of an HFP-containing monomer (for example, themethacrylate monomer 3,5-HFA-MA or the styryl monomer 3,5-HFA-St).Functional groups in HFP-containing monomers that can undergo directpolymerization (or polymerization with a comonomer) include acrylate,methacrylate, alpha, alpha, alpha-trifluoromethacrylate,alpha-halomethacrylate, acrylamido, methacrylamido, norbornene, vinyl,vinyl ether, and other groups known in the art. Examples of linkinggroups include C₁-C₁₂ alkyl, a C₁-C₁₂ heteroalkyl, ether group,thioether group, amino group, ester group, amide group, or a combinationthereof. Also contemplated are catalysts comprising chargedHFP-containing groups bound by ionic association to oppositely chargedsites on a polymer or a support surface.

The ROP reaction mixture comprises at least one organocatalyst and, whenappropriate, several organocatalysts together. The ROP catalyst is addedin a proportion of 1/20 to 1/40,000 moles relative to the cycliccarbonyl monomers, and preferably in a proportion of 1/1,000 to 1/20,000moles relative to the cyclic carbonyl monomers.

ROP Accelerators

The ROP polymerization can be conducted in the presence of an optionalaccelerator, in particular a nitrogen base. Exemplary nitrogen baseaccelerators are listed below and include pyridine (Py),N,N-dimethylaminocyclohexane (Me₂NCy), 4-N,N-dimethylaminopyridine(DMAP), trans 1,2-bis(dimethylamino)cyclohexane (TMCHD),1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD),7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), (−)-sparteine, (Sp)1,3-bis(2-propyl)-4,5-dimethylimidazol-2-ylidene (Im-1),1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (Im-2),1,3-bis(2,6-di-i-propylphenyl)imidazol-2-ylidene (Im-3),1,3-bis(1-adamantyl)imidazol-2-ylidene (Im-4),1,3-di-i-propylimidazol-2-ylidene (Im-5),1,3-di-t-butylimidazol-2-ylidene (Im-6),1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (Im-7),1,3-bis(2,6-di-i-propylphenyl)-4,5-dihydroimidazol-2-ylidene,1,3-bis(2,6-di-i-propylphenyl)-4,5-dihydroimidazol-2-ylidene (Im-8) or acombination thereof, shown in Table 5.

TABLE 5

In an embodiment, the accelerator has two or three nitrogens, eachcapable of participating as a Lewis base, as for example in thestructure (−)-sparteine. Stronger bases generally improve thepolymerization rate.

The catalyst and the accelerator can be the same material. For example,some ring opening polymerizations can be conducted using1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) alone, with no another catalystor accelerator present.

The catalyst is preferably present in an amount of about 0.2 to 20 mol%, 0.5 to 10 mol %, 1 to 5 mol %, or 1 to 2.5 mol %, based on totalmoles of cyclic carbonyl monomer.

The nitrogen base accelerator, when used, is preferably present in anamount of 0.1 to 5.0 mol %, 0.1 to 2.5 mol %, 0.1 to 1.0 mol %, or 0.2to 0.5 mol %, based on total moles of cyclic carbonyl monomer. As statedabove, in some instances the catalyst and the nitrogen base acceleratorcan be the same compound, depending on the particular cyclic carbonylmonomer.

The initiator groups are preferably present in an amount of 0.001 to10.0 mol %, 0.1 to 2.5 mol %, 0.1 to 1.0 mol %, or 0.2 to 0.5 mol %,based on total moles of cyclic carbonyl monomer.

In a specific embodiment, the catalyst is present in an amount of about0.2 to 20 mol %, the nitrogen base accelerator is present in an amountof 0.1 to 5.0 mol %, and the nucleophilic initiator groups of theinitiator are present in an amount of 0.1 to 5.0 mol % based on totalmoles of cyclic carbonate monomer.

The catalysts can be removed by selective precipitation or, in the caseof the solid supported catalysts, by filtration. The catalyst can bepresent in an amount of 0 wt % (weight percent) to about 20 wt %,preferably 0 wt % (weight percent) to about 0.5 wt % based on the totalweight of the cationic polymer and the residual catalyst. The cationicpolymer preferably comprises no residual catalyst.

Average Molecular Weight

The cationic polymers have a number average molecular weight (Mn) asdetermined by size exclusion chromatography of about 1500 to about50,000, more specifically about 1500 to about 30,000. The precursorpolymer to the cationic polymer and/or the cationic polymer preferablyhas a polydispersity index (PDI) of 1.01 to about 1.5, more particularly1.01 to 1.30, and even more particularly 1.01 to 1.25.

In some instances, the cationic polymers can self-assemble intonanoparticulate micelles in de-ionized water. The cationic polymers canhave a critical micelle concentration (CMC) of about 15 mg/L to about500 mg/L.

Utility

The micelles can have a minimum inhibitory concentration (MIC) formicrobial growth of about 7 mg/L to about 500 mg/L. The MIC can be belowthe CMC, meaning the antimicrobial activity is not dependent onself-assembly of the cationic polymers. In an embodiment, the cationicpolymer comprises a homopolymer of the cationic repeat.

Further disclosed is a method of treating a microbe, comprisingcontacting a microbe with a disclosed cationic polymer, thereby killingthe microbe.

For the examples below, the following definitions are applicable.

HC50 is defined as the concentration (in mg/L) of cationic polymer thatcauses 50% of mammalian red blood cells to undergo hemolysis. HC50values of 500 mg/L or higher are desirable.

HC20 is defined as the concentration (in mg/L) of cationic polymer thatcauses 20% of mammalian red blood cells to undergo hemolysis. HC20values of 500 mg/L or higher are desirable.

Minimum inhibitory concentration (MIC) is defined as the minimumconcentration (in mg/L) of cationic polymer required to inhibit growthof a given microbe for an eighteen hour period. A MIC less than 500 mg/Lis desirable. Even more desirable is a MIC of 250 mg/L or less. A lowerMIC indicates higher antimicrobial activity.

Minimum bactericidal concentration (MBC) is defined as the minimumconcentration (in mg/L) of cationic polymer required to kill a givenmicrobe at 99.9% efficiency over 18 hours. A lower MBC indicates higherantimicrobial activity.

HC50 selectivity is defined as the ratio of HC50/MIC. An HC50selectivity of 3 or more is desirable. Higher HC50 selectivity valuesindicate more activity against microbial cells and less toxicity tomammalian cells. Likewise, HC20 selectivity is defined as the ratio ofHC20/MIC. An HC20 selectivity of 3 or more is desirable.

Non-limiting microbes include Gram-positive Staphylococcus epidermidis(S. epidermidis), Gram-positive Staphylococcus aureus (S. aureus),Gram-negative Escherichia coli (E. coli), Gram-negative Pseudomonasaeruginosa (P. aeruginosa), fungus Candida albicans (C. albicans),Gram-positive Methicillin-resistant Staphylococcus aureus (MRSA),Gram-positive Vancomycin-resistant Enterococcus (VRE), Gram-negativeAcinetobacter baumannii (A. baumannii), yeast Cryptococcus neoformans(C. neoformans), and Gram-negative Klebsiella pneumoniae (K.pneumoniae).

The cationic polymers are generally non-hemolytic up to 1000 mg/L (1000ppm). The cationic polymers can also be non-cytotoxic at concentrationsup to 1000 micrograms per milliliter. In some cases, cell viability ofhuman fibroblast cells incubated with the cationic polymers was morethan 90%. The cationic polymers can also inhibit or eradicate a biofilm.

The biodegradability, low average mass, high antimicrobial activity, andlow cytotoxicity make these cationic polymers highly attractive for awide range of medical and household uses, including wound treatments,treatment of infections, antibiotic drugs, and disinfectants forhousehold and hospital surfaces and medical instruments. In anembodiment, a medical composition comprises one or more of the disclosedcationic polymers. The medical composition can comprise water, and theconcentration of the cationic polymer can be below the critical micelleconcentration of the cationic polymer. The medical composition can be adrug. The drug can be a solution, gel, powder, pill, paste, or ointment.The drug can be delivered orally, by injection, by spray, by inhalant,by dermal patch, and/or as a topically applied ointment.

The following examples demonstrate the preparation and properties of thecationic polymers.

EXAMPLES

Materials used in the following examples are listed in Table 6.

TABLE 6 ABBREVIATION DESCRIPTION SUPPLIER Me-DEA N-methyl DiethanolamineSigma-Aldrich Bu-DEA N-Butyl Diethanolamine Sigma-Aldrich Bn-DEAN-Benzyl Diethanolamine Sigma-Aldrich tBu-DEA N-tert-ButylDiethanolamine Sigma-Aldrich Ph-DEA N-Phenyl DiethanolamineSigma-Aldrich Ac-DEA N-Acetyl Diethanolamine prepared below BOC-DEAN-BOC Diethanolamine Sigma-Aldrich Diethylene Glycol Sigma-Aldrich2,2′-Thiodiethanol Sigma-Aldrich 1,5-Pentanediol Sigma-Aldrich DBUl,8-Diazabicyclo[5,4,0]undec-7-ene Sigma-Aldrich p-Chloromethyl BenzylAlcohol Sigma-Aldrich TMA Trimethylamine Sigma-Aldrich DCMDichloromethane Sigma-Aldrich

Herein, Mn is the number average molecular weight, Mw is the weightaverage molecular weight, and MW is the molecular weight of onemolecule.

N-(3,5-trifluoromethyl)phenyl-N′-cyclohexyl-thiourea (TU) was preparedas reported by R. C. Pratt, B. G. G. Lohmeijer, D. A. Long, P. N. P.Lundberg, A. Dove, H. Li, C. G. Wade, R. M. Waymouth, and J. L. Hedrick,Macromolecules, 2006, 39 (23), 7863-7871, and dried by stirring in dryTHF over CaH₂, filtering, and removing solvent under vacuum.

Monomer Synthesis

N-Acetyl diethanolamine was prepared according to the followingprocedure. A flask was charged with diethanolamine (10 g, 95.1 mmol),triethylamine (13.3 mL, 95.1 mmol) and methanol (75 mL). The reactionmixture was cooled to 0° C. and acetic anhydride (9.2 g, 90.0 mmol) wasadded dropwise. The mixture was stirred 2 hours, warmed to roomtemperature, and allowed to stir overnight. Volatiles were removed, thecrude product was dissolved in ethyl acetate (100 mL) and washed with10% HCl (3×), saturated potassium carbonate (3×) and brine. The solventwas removed yielding 9.2 g (66%) yellow oil.

BnMPA has the following structure:

BnMPA and other cyclic carbonate monomers can be prepared from2,2-bis(methylol)propionic (BisMPA) according to Scheme 1.

BisMPA can be converted (i) to the benzyl ester BnMPA using knownmethods. Reaction of BnMPA with triphosgene (ii) produces cycliccarbonyl monomer, MTCOBn. Debenzylation of MTCOBn (iii) produces5-methyl-5-carboxyl-1,3-dioxan-2-one (MTCOH). Two pathways are shown forforming an ester from MTCOH. In the first pathway, (iv), MTCOH istreated with a suitable carboxy activating agent, such asdicyclohexylcarbodiimide (DCC), which reacts with ROH to form MTCOR in asingle step. Alternatively, MTCOH can be converted first (v) to the acidchloride MTCCl followed by treatment (vi) of MTCCl with ROH in thepresence of a base to form MTCOR. Both pathways are illustrative and arenot meant to be limiting. The following conditions are typical for thereactions shown in Scheme 1: (i) Benzylbromide (BnBr), KOH, DMF, 100°C., 15 hours, 62% yield of BnMPA; (ii) triphosgene, pyridine, CH₂C₁₂,−78° C. to 0° C., 95% yield of MTCOBn; (iii) Pd/C (10%), H₂ (3 atm),EtOAc, room temperature, 24 hours, 99% yield of MTCOH; (iv) ROH, DCC,THF, room temperature, 1 to 24 hours; (v) (COCl)₂, THF, roomtemperature, 1 hour, 99% yield of MTCCl; (vi) ROH, NEt₃, roomtemperature, 3 hours yields MTCOR.

Example 1 Preparation of 6-methyl-1,3,6-dioxazocan-2-one (DXA-Me)

A round bottom flask was charged with N-methyl diethanolamine (10.0 g,83.9 mmol), triethylamine (24.0 mL, 167.8 mmol), dry tetrahydrofuran(THF) (600 mL) and stirbar. The reaction flask was cooled to −20° C.under a nitrogen atmosphere. Separately, triphosgene (8.3 g, 28.8 mmol)was dissolved in dry THF (100 mL) and added slowly to the reactionmixture. A white precipitate formed instantly and stirring was continuedfor another 2 hours maintaining a reaction temperature less than 10° C.Diethyl ether (800 mL) was added to further precipitate any remainingHCl salts followed by filtration of the heterogeneous solution. Thefiltrate was concentrated yielding a yellow/brown oil product (10.4 g,85%).

Example 2 Preparation of 6-butyl-1,3,6-dioxazocan-2-one (DXA-Bu)

The procedure of Example 1 was followed using N-butyl diethanolamine(13.5 g, 83.9 mmol), triethylamine (24.0 mL, 167.8 mmol), dry THF (600mL) and triphosgene (8.3 g, 28.8 mmol). The filtrate was concentratedyielding a yellow/brown oil product (12.9 g, 82%).

Example 3 Preparation of 6-benzyl-1,3,6-dioxazocan-2-one (DXA-Bn)

The procedure of Example 1 was followed using N-benzyl diethanolamine(16.4 g, 83.9 mmol), triethylamine (24.0 mL, 167.8 mmol), dry THF (600mL) and triphosgene (8.3 g, 28.8 mmol). The filtrate was concentratedyielding a yellow oil product (14.5 g, 78%).

Comparative Example 4 Preparation of 6-tert-butyl-1,3,6-dioxazocan-2-one(DXA-tBu)

The procedure of Example 1 was followed using N-tert-butyldiethanolamine (16.4 g, 83.9 mmol), triethylamine (24.0 mL, 167.8 mmol),dry THF (600 mL) and triphosgene (8.3 g, 28.8 mmol). The filtrate wasconcentrated yielding a clear oil containing a non-isolable amount ofproduct within a mixture of oligomeric diethanolamines.

Example 5 Preparation of 6-phenyl-1,3,6-dioxazocan-2-one (DXA-Ph)

The procedure of Example 1 was followed using N-phenyldiethanolamine(15.2 g, 83.9 mmol), triethylamine (24.0 mL, 167.8 mmol), dry THF (600mL) and triphosgene (8.3 g, 28.8 mmol). The filtrate was concentratedyielding a clear oil containing a mixture of products. The product waspurified using a column chromatography EtOAc:Hexanes (3:1) yielding 3.3g (19%) of a clear oil which turned brown over time.

Comparative Example 6 Attempted Preparation of6-acetyl-1,3,6-dioxazocan-2-one (DXA-Ac)

The procedure of Example 1 was followed using N-acetyl diethanolamine(12.3 g, 83.9 mmol), triethylamine (24.0 mL, 167.8 mmol), dry THF (600mL) and triphosgene (8.3 g, 28.8 mmol). The filtrate was concentratedyielding only oligomeric compounds.

Comparative Example 7 Attempted Preparation of6-Boc-1,3,6-dioxazocan-2-one (DXA-Boc)

The procedure of Example 1 was followed using N-boc diethanolamine (3 g,14.6 mmol), triethylamine (4.1 mL, 29.2 mmol), dry dichloromethane (100mL) and triphosgene (1.4 g, 4.9 mmol). The filtrate was concentratedyielding only oligomeric compounds.

Comparative Example 8 Attempted Preparation of 1,3,6-trioxocan-2-one(TXA)

The procedure of Example 1 was followed using diethylene glycol (8.9 g,83.9 mmol), triethylamine (24.0 mL, 167.8 mmol), dry THF (600 mL) andtriphosgene (8.3 g, 28.8 mmol). The filtrate was concentrated yieldingonly oligomeric compounds.

Comparative Example 9 Attempted Preparation of 1,3,6-dioxathiocan-2-one(DXT)

The procedure of Example 1 was followed using 2,2′-thiodiethanol (10.2g, 83.9 mmol), triethylamine (24.0 mL, 167.8 mmol), dry THF (600 mL) andtriphosgene (8.3 g, 28.8 mmol). The filtrate was concentrated yieldingonly oligomeric compounds.

Comparative Example 10 Attempted Preparation of Pentamethylene Carbonate(PMC)

The procedure of Example 1 was followed using 1,5-pentanediol (1 g, 9.6mmol), triethylamine (2.8 mL, 20.2 mmol), dry THF (100 mL) andtriphosgene (0.96 g, 3.24 mmol). The filtrate was concentrated yieldingonly oligomeric compounds.

Cyclizations of the above diols were also attempted using ethylchloroformate, and bis(pentafluorophenyl) carbonate (PFC). Table 7summarizes the results.

TABLE 7 Cyclic Cycli- Cyclization Yield (%) Product zation EthylPolymer- Example Diol Product Triphosgene Chloroformate PFC izable? 1N-Methyl diethanolamine DXA-Me 85  >95  >95  yes 2 N-Butyldiethanolamine DXA-Bu 82  n/a n/a yes 3 N-Benzyl diethanolamine DXA-Bn78  n/a n/a yes 4 N-tert-Butyl diethanolamine DXA-tBu 0 0 0 n/a 5N-Phenyl diethanolamine DXA-Ph 19^(a) 0 0 yes 6 N-Acetyl diethanolamineDXA-Ac 0 0 0 n/a 7 N-Boc-diethanolamine DXA-Boc 0 0 0 n/a 8 DiethyleneGlycol TXA 0 0 0 n/a 9 Thiodiethanol DXT 0 0 0 n/a 10 1,5-pentanediolPMC 0 0 0 n/a ^(a)multiple derivatives reported ^(b) n/a = not attempted

Using the following structure as a guide,

the results in Table 7 indicate that cyclization to form 8-memberedcyclic carbonates using triphosgene, bis(pentafluorophenyl) carbonate,and ethyl chloroformate is favored when X′ is nitrogen and Y′ is amethyl group or a group comprising a methylene group linked directly toX′.

Ring Opening Polymerizations Examples 11-14 Preparation of P-4, Example14 is Representative

In a nitrogen filled glove box a vial was charged with BnMPA (0.0039 g,0.0172 mmol), 6-methyl-1,3,6-dioxazocan-2-one (0.5 g, 3.44 mmol),dichloromethane (1.5 g) and a stirbar. The polymerization was initiatedvia addition of DBU (0.016 mL, 0.1 mmol). After complete monomerconversion (˜18 hours) the reaction mixture was precipitated intodiethyl ether and collected by centrifugation yielding 0.48 g (96%)white amorphous polymer (Mn 20 kDa; PDI 1.14, n=200).

Using the above procedure, a molecular weight series was generated byvarying the amount of initiator BnMPA with respect to the cycliccarbonate monomer DXA-Me, summarized in Table 8 below. FIG. 1 is a graphof Mn as a function of average degree of polymerization (DP) forpolymers P-1 to P-4.

Example 15 Preparation of P-5

Polymer P-5 was prepared using DXA-Bu and Me-DEA as the dinucleophilicinitiator. In a nitrogen filled glovebox a vial was charged with Me-DEA(0.0032 g, 0.026 mmol), DXA-Bu (1.0 g, 5.34 mmol) and DCM (1.5 g). Thepolymerization was initiated by the addition of DBU (0.080 mL, 0.53mmol). The reaction mixture was stirred until complete monomerconsumption followed by immediate precipitation into ether, yielding0.91 g (90%) of off-white polymer; Mn=30.0 kDa, PDI-1.22, n=200.

Example 16 Preparation of P-6

Polymer P-6 was prepared using DXA-Bn and tBu-DEA as the dinucleophilicinitiator. In a nitrogen filled glovebox a vial was charged with tBu-DEA(0.0044 g, 0.027 mmol), DXA-Bn (0.30 g, 1.35 mmol) and DCM (0.65 g). Thepolymerization was initiated by the addition of DBU (0.021 mL, 0.135mmol). The reaction mixture was stirred until complete monomerconsumption followed by immediate precipitation into ether, yielding0.28 g (93%) of off-white polymer; Mn=17.5 kDa, PDI-1.36, n=50.

Table 8 summarizes polymers P-1 to P-6. DP is the average degree ofpolymerization, Mn is the number average molecular weight, PDI ispolydispersity (Mw/Mn).

TABLE 8 Monomer Initiator Yield DP Example Name Monomer (mmol) Initiator(mmol) (%) (n) Mn PDI 11 P-1 DXA-Me 3.44 BnMPA 0.0172 93 20 3646 1.09 12P-2 DXA-Me 3.44 BnMPA 0.0172 95 50 7924 1.09 13 P-3 DXA-Me 3.44 BnMPA0.0172 95 100 13544 1.11 14 P-4 DXA-Me 3.44 BnMPA 0.0172 92 200 253001.17 15 P-5 DXA-Bu 3.44 Me-DEA 0.0172 90 50 11600 1.22 16 P-6 DXA-Bn3.44 tBu-DEA 0.0172 93 50 17500 1.36

Quaternization Examples 17-19

The following procedure to form quaternary polymer Q-3 from P-4 (Example19) is representative.

A vial was charged with P-4 (1 g, 8.4 mmol eq.), DMF (10 mL) and astirbar. Excess methyl iodide (2.4 g, 16.8 mmol) was added and thereaction mixture stirred for 6 hours under ambient conditions. Themixture was then slowly added to stirred THF causing the polymer toprecipitate as an off-white amorphous solid, which was dried undervacuum (2.3 g, 95%).

Using the above procedure, polymers P-2 and P-3 were also quaternizedwith methyl iodide (MeI) to form polymers Q-1 and Q-2, respectively.Table 9 summarizes the quaternary polymers formed.

TABLE 9 Initial DP MeI Quaternization Example Name Polymer (n) (equiv)(%) 17 Q-1 P-2 50 2 >99 18 Q-2 P-3 100 2 >99 19 Q-3 P-4 200 2 >99

Biological Measurements Minimal Inhibitory Concentration (MIC)

Gram-positive Staphylococcus aureus (S. aureus, ATCC No. 29737),Gram-negative Escherichia coli (E. coli, ATCC No. 25922), Gram-negativePseudomonas aeruginosa (P. aeruginosa, ATCC No. 9027), and Candidaalbicans (C. albicans, a fungus, (ATCC No. 10231) were re-constitutedfrom the lyophilized form. Bacterial samples were cultured in trypticsoy broth (TSB) at 37° C. under constant shaking of 300 rpm. The MICs ofthe polymers were measured using the broth microdilution method. 100microliters of tryptic soy broth (TSB) containing a polymer at variousconcentrations was placed into each well of a 96-well tissue cultureplate. An equal volume of bacterial suspension (3×10⁵ CFU/ml), where CFUmeans colony forming units, was added into each well. Prior to mixing,the bacterial sample was first inoculated overnight to enter its loggrowth phase. The concentration of bacterial solution was adjusted togive an initial optical density (O.D.) reading of approximately 0.07 at600 nm wavelength on microplate reader (TECAN, Switzerland), whichcorresponds to the concentration of McFarland 1 solution (3×10⁸ CFU/ml).The bacterial solution was further diluted by 1000 times to achieve aninitial loading of 3×10⁵ CFU/ml. The 96-well plate was kept in anincubator at 37° C. under constant shaking of 300 rpm for 18 hours. TheMIC was taken as the concentration of the antimicrobial polymer at whichno microbial growth was observed with unaided eyes and microplate reader(TECAN, Switzerland) at the end of 18 hours incubation. Broth containingmicrobial cells alone was used as negative control, and each test wascarried out in 6 replicates.

Table 10 lists the MIC (mg/L), HC50 (mg/L), and HC selectivity valuesfor the cationic polymers Q-1 to Q-3 (Examples 17-19) against S. aureus,E. coli, P. aeruginosa, and C. albicans.

TABLE 10 Hemolysis DP MIC (mg/L) selectivity Example Name (n) S. aureusE. coli P. aeruginosa C. albicans HC₅₀ (HC₅₀/MIC) 12 P-250 >1000 >1000 >1000 >1000 >1000 ND 13 P-3100 >1000 >1000 >1000 >1000 >1000 ND 14 P-4200 >1000 >1000 >1000 >1000 >1000 ND 17 Q-1 50 31 250 250 63 >1000 >4.0to >32.3 18 Q-2 100 31 63 250 63 >1000 >4.0 to >32.3 19 Q-3 200 31 63125 63 >1000 >8.0 to >32.3 ND = not determined

Lower MIC (500 mg/L or less) and higher HC50 (500 mg/L or more)represent preferred performance. An HC selectivity (HC50/MIC) value of 3or more is also preferred. Each of the polymers was active against eachof the four microbes, with Q-3 being the most active based on relativeperformance against P. aeruginosa.

Hemolytic Activity Testing of Cationic Polymers

Fresh rat blood cells were subjected to 25× dilution with phosphatebuffered saline (PBS) to obtain an approximate 4% v/v suspension for usein this experiment. Red blood cell suspension (300 microliters) wasadded to each tube containing an equal volume (300 microliters) ofpolymer solution in PBS (with final polymer concentrations ranging from3.9 mg/L to 1000 mg/L). The tubes were then incubated at 37° C. for 1hour before they were centrifuged at 1000×g (g=relative centrifugalforce) for 5 minutes. Aliquots (100 microliters) of supernatant weretransferred to each well of a 96-well plate and analyzed for hemoglobinrelease at 576 nm using a microplate reader (TECAN, Switzerland). Redblood cells suspension incubated with PBS was used as negative control.Absorbance of red blood cells lyzed with 0.1% v/v Triton X-100 was usedas the positive control and taken to be 100% hemolytic. Percentage ofhemolysis was calculated using the following formula:

Hemolysis (%)=[(O.D._(576 nm) of treated sample−O.D.₅₇₆ nm of negativecontrol)/(O.D.₅₇₆ nm of positive control−O.D.₅₇₆ nm of negativecontrol)]×100.

Data are expressed as mean±standard deviations of 4 replicates.

FIG. 2 is a graph showing the % hemolysis of rat red blood cells as afunction of concentration (mg/L) of cationic polymer Examples 21-23 (Q-1to Q-3). About 0% hemolysis was observed for each of these polymers upto the highest concentration of 1000 ppm.

Cytotoxicity Testing of Cationic Polymers

Human dermal fibroblast (HDF) cells or human embryonic kidney (HEK293)cells were maintained in DMEM growth medium supplemented with 10% fetalbovine serum (FBS), sodium pyruvate, 100 U/mL penicillin and 100 mg/mLstreptomycin and cultured at 37° C. under an atmosphere of 5% CO₂ and95% humidified air. The cytotoxicity of polymers Q-1 to Q-3 against eachcell line was studied using the standard3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assayprotocol. HDF cells (or HEK293) were seeded onto 96-well plates at adensity of 1×10⁴ cells per well and allowed to adhere overnight. Thepolymers were first dissolved in high pressure liquid chromatography(HPLC) grade water and serially diluted using Dulbecco's Modified EagleMedium (DMEM) growth medium to achieve polymer concentrations rangingfrom 3.9 mg/L to 1000 mg/L with water concentration fixed at 10% v/v foreach condition. Polymer solution (100 microliters) was added to thecells in each well, and the plate was allowed to incubate for 48 hoursat 37° C. Subsequently, 100 microliters of growth media and 10microliters of MTT solution (5 mg/ml in PBS) were added to each well andthe cells were incubated for 4 hours at 37° C. according to themanufacturer's directions. Resultant formazan crystals formed in eachwell were solubilized using 150 microliters of dimethylsulfoxide (DMSO)upon removal of growth media, and the absorbance was determined using amicroplate spectrophotometer at wavelengths of 550 nm and 690 nm.Relative cell viability was expressed as[(A₅₅₀−A₆₉₀)_(sample)/(A₅₅₀−A₆₉₀)_(control)]×100%. Data are expressed asmean±standard deviations of 3 to 4 replicates per polymer concentration.

FIG. 3 is a bar graph showing the percent cell viability of HDF andHEK293 cells as a function of cationic polymer concentration. Higherpercent cell viability values are desirable at a given concentration.Each of Q-1 to Q-3 was non-toxic to both cell lines at allconcentrations up to 1000 micrograms per milliliter.

Killing Efficiency of Cationic Polymers

Similar to MIC testing, 100 microliters of TSB containing a polymer atvarious concentrations (0, MIC and 2.0MIC) were placed into each well ofa 96-well tissue culture plate. An equal volume of bacterial suspension(3×10⁵ CFU/ml), where CFU means colony forming units, was added intoeach well. Prior to mixing, the bacterial sample was first inoculatedovernight to enter its log growth phase. The concentration of bacterialsolution was adjusted to give an initial optical density (O.D.) readingof approximately 0.07 at 600 nm wavelength on a microplate reader(TECAN, Switzerland), which corresponds to the concentration ofMcFarland 1 solution (3×10⁸ CFU/ml). The bacterial solution was furtherdiluted by 1000 times to achieve an initial loading of 3×10⁵ CFU/ml. The96-well plate was kept in an incubator at 37° C. under constant shakingof 300 rpm for 18 hours. The respective samples were then subjected to aseries of ten-fold dilutions and plated onto lysogeny broth (LB) agarplates. The plates were then incubated overnight and counted forcolony-forming units. A sample containing microbes treated with brothcontaining 10% v/v water was used as a control.

FIGS. 4 to 7 are graphs showing the relationship between colony formingunits/mL of S. aureus, E. coli, P. aeruginosa, and C. albicans as afunction of Q-3 concentration, respectively. For each microbe, the CFUcount was zero at a cationic polymer concentration of 1×MIC. Thus, Q-3achieved 99.999% killing efficiency at 1×MIC (i.e., the MBC is equal tothe MIC).

Time-Kill Studies

S. aureus, C. albicans, and E. coli were treated with Q-3 at 1, 2, 4,and 8×MIC for up to 18 hours. The bar charts of FIGS. 8 to 10 show thatQ-3 achieved 99.9% killing efficiency at 8×MIC and 1 minute. No growthwas observed for S. aureus out to 18 hours (inset of FIG. 8).

FIG. 11 is a bar graph showing the biomass of biofilm of E. coli and S.aureus as a function of Q-3 concentration (2, 4, 8, 10, 12, and 16×MIC).The percent cell viability of E. coli and S. aureus at eachconcentration are plotted in FIG. 12 for comparison. Q-3 lysed S. aureusand E. coli biofilms effectively at 8×MIC after a single treatment.

Mechanism of Antimicrobial Properties

The morphological changes of S. aureus and E. coli cells were observedby FE-SEM after treatment with the cationic polymer Q-3 for 2 hours. Ascan be seen in the magnification series of scanning electron microscope(SEM) images of FIG. 13, treatment of S. aureus with Q-3 at a lethalconcentration (250 mg/L) for 2 hours results in significant membranedamage to S. aureus (right-most image). The SEM images of FIG. 14 showthe treatment of E. coli with Q-3 at a lethal concentration (500 mg/L)for 2 hours also results in significant membrane damage to (right-mostimage). These results indicate that Q-3 interacts with the membrane ofbacterial and yeast cells by forming pores and eventually leads todisruption of the bacterial and yeast membranes.

CONCLUSION

Biodegradable cationic polycarbonates having a main chain quaternarynitrogen were prepared and shown to be highly effective in killingGram-positive and Gram-negative microbes. The cationic polymers are alsoeffective in inhibiting or eradicating biofilms at low concentration.The cationic polymers can be non-hemolytic and non-cytotoxic.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. When a range is used to express apossible value using two numerical limits X and Y (e.g., a concentrationof X ppm to Y ppm), unless otherwise stated the value can be X, Y, orany number between X and Y.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and their practical application, and toenable others of ordinary skill in the art to understand the invention.

What is claimed is:
 1. A cationic polymer of formula (6):I″-[Q′-E″]n′  (6), wherein n′ is a positive integer greater than orequal to 1, each Q′ is an independent divalent polymer chain, I″ has avalency of n′, I″ comprises 1 or more carbons, and I″ comprises n′heteroatoms independently selected from the group consisting of oxygen,nitrogen, and sulfur, wherein each of the heteroatoms is linked to arespective Q′ terminal backbone carbonyl group, each E″ is a monovalentend group selected from the group consisting of hydrogen and moietiescomprising 1 to 50 carbons, wherein each E″ is linked to a respective Q′terminal backbone oxygen, each Q′ comprises a cationic repeat unit offormula (7):

wherein each R′ is hydrogen, R″ is a group comprising 1 or more carbons,wherein one carbon of R″ is bonded to the positive charged nitrogen,*—CH₂—Y′ is a monovalent radical selected from the group consisting ofmethyl, ethyl, propyl, butyl, benzyl, and substituted benzyl, X^(⊖) is anegative-charged counterion.
 2. The cationic polymer of claim 1, whereinI″ is a residue of an initiator for a ring opening polymerization usedto form Q′.
 3. The cationic polymer of claim 1, wherein Q′ is apolycarbonate homopolymer of the cationic repeat unit.
 4. The cationicpolymer of claim 1, wherein n′ is 1 and I″ is a residue of amono-nucleophilic initiator used to form Q′ by ring openingpolymerization.
 5. The cationic polymer of claim 1, wherein each Q′ hasan average degree of polymerization of between 1 and
 200. 6. Thecationic polymer of claim 1, wherein each E″ is hydrogen.
 7. Thecationic polymer of claim 1, wherein R″ is methyl.
 8. The cationicpolymer of claim 1, wherein *—CH₂—Y′ is methyl.
 9. The cationic polymerof claim 1, wherein *—CH₂—Y′ is ethyl.
 10. The cationic polymer of claim1, wherein *—CH₂—Y′ is propyl.
 11. The cationic polymer of claim 1,wherein *—CH₂—Y′ is butyl.
 12. The cationic polymer of claim 1, wherein*—CH₂—Y′ is benzyl.
 13. The cationic polymer of claim 1, wherein X^(⊖)is a halide selected from the group consisting of chloride, bromide, andiodide.
 14. The cationic polymer of claim 1, wherein the cationicpolymer is derived by ring opening polymerization of a compound offormula (1):

wherein each R′ is hydrogen, and *—CH₂—Y′ is selected from the groupconsisting of methyl, ethyl, propyl, butyl, benzyl, and substitutedbenzyl.
 15. The cationic polymer of claim 1, wherein the cationicpolymer is an effective antimicrobial agent against a microbe selectedfrom the group consisting of Gram-negative microbes, Gram-positivemicrobes, yeast, fungi, and combinations thereof.
 16. The cationicpolymer of claim 1, wherein the cationic polymer is effective ininhibiting growth of a biofilm.
 17. The cationic polymer of claim 1,wherein the cationic polymer has an HC50 value greater than 1000 mg/L.18. A method of killing a microbe, comprising contacting the microbewith the cationic polymer of claim
 1. 19. A medical compositioncomprising one or more of the cationic polymers of claim
 11. 20. Acationic polymer of formula (8):E″-Q′-I″-Q′-E″  (8), wherein each Q′ is an independent divalent polymerchain, I″ is a divalent radical comprising 1 or more carbons, and I″comprises 2 heteroatoms independently selected from the group consistingof oxygen, nitrogen, and sulfur, wherein each of the heteroatoms islinked to a respective Q′ terminal backbone carbonyl group, each E″ isan independent monovalent end group selected from the group consistingof hydrogen and moieties comprising 1 to 50 carbons, wherein each E″ islinked to a respective Q′ terminal backbone oxygen, each Q′ comprises acationic repeat unit of formula (7):

wherein each R′ is hydrogen, R″ is a group comprising 1 or more carbons,wherein one carbon of R″ is bonded to the positive charged nitrogen,*—CH₂—Y′ is a monovalent radical selected from the group consisting ofmethyl, ethyl, propyl, butyl, benzyl, and substituted benzyl, and X^(⊖)is a negative-charged counterion.